U.C. police were mostly inside the student union and on a balcony overhead during the violence, rarely venturing into the crowd.

Since then in the city of Berkeley extreme groups have squared off twice in a downtown park, exchanging punches.

There were 20 arrests last time, but some claim the riot-clad Berkeley officers didn't do enough. "There have been moments, when police are there and they appear to be doing nothing," Berkeley Police Chief Andrew Greenwood said. "You can go on YouTube and see how close people have gotten to felony assaults. That's challenging for the police to inject force into because we're held accountable for every use of force, on every person."

Though U.C. Berkeley administration and police don't know exactly what to expect Thursday, officials told us they may use a different strategy this time.